temporal vision
TRANSCRIPT
Frequency= Cycles/second = Hertz
Relative Sensitivity
• Low modulation steady (non-flickering) stimulus
• High modulation flickering stimulus
• Relative Sensitivity = 1/ (% Modulation)
• As the % modulation increases , the relative sensitivity decreases
No flicker
Threshold
Critical Flicker Frequency
• For a specific % modulation, temporal frequency is increased until the stimulus does not flicker (fuses)
• This is called CFF = Critical Flicker Frequency
Low frequency CFF
Hi frequency CFF
No flicker Flicker No flicker
High Low
• Loss at low frequencies
– Troxler phenomenon
– Purkinje tree visualization
Troxlex phenomenon
• http://upload.wikimedia.org/wikipedia/commons/6/6e/Lilac-Chaser.gif
• Loss at high frequencies
Ferry-Porter law: CFF increase with log of retinal illumination
Broca-Sultzer effect
Stimuli with duration between 50 and 100 ms are perceived brighter than shorter or longer stimuli
Brucke-Bartley Effect: A flickering 10 HZ light appears brighter than a steady light of the same luminance (example of Broca- Sultzereffect)
Talbot-Plateau law: brightness of a fused temporally modulated stimulus is equal to the brightness of a steady light of the same average luminance
Masking
• Simultaneous masking
– Example: Crowding phenomenon in amblyopes
• Backward masking
– Example: Metacontrast
• Forward masking